CN111058063B

CN111058063B - Electrolytic copper foil, electrode comprising same, and lithium ion battery comprising same

Info

Publication number: CN111058063B
Application number: CN201811200604.5A
Authority: CN
Inventors: 赖耀生; 黄建铭; 郑桂森; 周瑞昌
Original assignee: Chang Chun Petrochemical Co Ltd
Current assignee: Chang Chun Petrochemical Co Ltd
Priority date: 2018-10-16
Filing date: 2018-10-16
Publication date: 2021-02-02
Anticipated expiration: 2038-10-16
Also published as: CN111058063A; ES2836711T3; EP3640371A1; PL3640371T3; HUE052191T2; EP3640371B1

Abstract

The invention provides an electrolytic copper foil, an electrode comprising the electrolytic copper foil and a lithium ion battery comprising the electrolytic copper foil. The electrolytic copper foil is provided with a roller surface and a deposition surface which are opposite; wherein the nanoindentation surface hardness of the roll face is equal to or greater than 0.5 gigapascals and equal to or less than 3.5 gigapascals; and the lightness of the roll surface is equal to or greater than 25 and equal to or less than 75. In addition, an electrode comprising the electrolytic copper foil and a lithium ion battery comprising the electrolytic copper foil are also provided.

Description

Electrolytic copper foil, electrode comprising same, and lithium ion battery comprising same

Technical Field

The present invention relates to an electrolytic copper foil, and more particularly to an electrolytic copper foil for an electrode of a lithium ion battery. In addition, the invention also relates to a lithium ion battery containing the electrolytic copper foil.

Background

With the rapid increase in the demand for mobile electronic devices, Electric Vehicles (EVs), Hybrid Electric Vehicles (HEVs), and the like, rechargeable Lithium Ion Batteries (LiBs) having high power density and long cycle life have attracted considerable attention, and the use of copper foil having both good toughness and electrical conductivity as an electrode of a lithium ion battery is one of the major points in the development of lithium ion batteries.

The copper foil for the lithium ion battery may be classified into a rolled copper foil or an electrolytic copper foil according to the preparation method, but the rolled copper foil has high processing cost and limited width due to the need of multiple rolling, annealing and other process steps, and thus the copper foil for the lithium ion battery mainly employs an electrolytic copper foil which is low in manufacturing cost and can be thinned.

When the electrolytic copper foil is selected to prepare the electrode, the surface of the electrolytic copper foil is coated with the active material and rolled, and according to the coating condition and the rolling condition of the active material layer, the copper foil can be damaged such as wrinkles and cracks, even the copper foil is broken, so that the yield of battery manufacture is greatly reduced, and the cycle characteristic of the battery is reduced. Therefore, taiwan patent publication No. 201728764 discloses an electrolytic copper foil having durability by defining a ratio of tensile strengths at two different stretching speeds. Although the above electrolytic copper foil is expected to improve the cycle life of the lithium ion battery, after the surface of the electrolytic copper foil is coated with the active material, the junction between the area coated with the active material and the area not coated with the active material on the electrolytic copper foil can bear different pressures during rolling treatment, which may cause the fracture of the junction of the electrolytic copper foil after rolling treatment, and even affect the production yield.

Disclosure of Invention

In view of the technical defects of the electrolytic copper foil, the present invention aims to provide an electrolytic copper foil with good mechanical properties, which reduces the problem of cracking of the electrolytic copper foil and improves the production yield.

To achieve the above object, the present invention provides an electrolytic copper foil having a roll surface (dry side) and a deposited side (deposited side) opposite to each other; wherein the nanoindentation surface hardness of the roll face is equal to or greater than 0.5 gigapascals (GPa) and equal to or less than 3.5 GPa; and the lightness of the roll surface is equal to or greater than 25 and equal to or less than 75.

According to the invention, by limiting the surface hardness range and the lightness range of the nano indentation of the roller surface of the electrolytic copper foil, the electrolytic copper foil can bear stress generated by rolling when a battery is manufactured, and the phenomena of creasing and breaking are reduced and even avoided, so that the yield of the electrolytic copper foil applied to the production of lithium ion batteries is improved. In addition, the electrolytic copper foil reduces or even avoids wrinkles and fractures, can improve the cycle characteristic of the lithium ion battery, and has longer battery life.

The electrolytic copper foil is obtained by taking an aqueous solution with sulfuric acid and copper sulfate as main components as an electrolyte, usually adopting a titanium plate coated by iridium element or oxide thereof as an anode (DSA), taking a titanium roller as a cathode roller (cathode drum), electrifying direct current between the two electrodes to electrolyze and separate copper ions in the electrolyte on the cathode roller, and then stripping and continuously rolling the separated electrolytic copper foil from the surface of the cathode roller; wherein, the surface of the electrolytic copper foil contacting with the cathode roller surface is called a roller surface, and the other surface opposite to the roller surface is called a deposition surface. Generally, the state of the surface of a cathode roller during electric initial electroplating can obviously influence the hardness of the roller surface of the electrolytic copper foil; when the electrolytic copper foil is stripped from the cathode roller, the roller surface which is originally tightly attached to the electrolytic copper foil is exposed in the air, the exposure time depends on the rotating speed of the cathode roller, when the electrolytic copper foil with thicker thickness is produced, the rotating speed of the cathode roller is slower, so that the time for exposing the surface of the cathode roller in the air is longer, the surface of the cathode roller is in a very dry state, and when the cathode roller is contacted with electrolyte again, the wetting degree of the surface of the cathode roller is inconsistent, so that the hardness of the roller surface of the electrolytic copper foil is reduced; through multiple researches of the inventor, the inventor finds that the electrolyte is sprayed on the surface of the cathode roller to wet the surface just before the roller enters the electrolyte, so that the hardness of the roller surface of the prepared electrolytic copper foil is improved.

In addition, compared with the prior art that the electrolytic copper foil needs to form a multi-layer structure (such as two layers or three layers) with different components or different hardness in sequence to achieve the required properties, the invention can lead the electrolytic copper foil to have the expected mechanical properties without repeating the foil manufacturing process for many times, thereby being suitable for lithium ion batteries and further having the advantage of commercialization.

Preferably, the nano-indentation surface hardness of the roller surface is equal to or more than 1.0GPa and equal to or less than 3.0 GPa.

The Lightness (L) is one of three attributes of a color in the color system described in JIS Z8729, and represents that the lighter the color is, the closer to white the higher the Lightness is. The brightness of the electrolytic copper foil is related to the surface morphology of the roll, and when the degree of roll oxidation is increased, the brightness of the roll surface of the electrolytic copper foil is decreased. Therefore, in order to remove the oxide layer generated on the surface of the cathode drum, the surface of the cathode drum is repolished after a certain production length (typically five to ten thousand meters) by using an in-line grinding wheel; the grinding wheel is divided into different types according to the grain size of grinding particles, the smaller the number of the type is, the larger the grain size of the grinding particles is, the grinding wheel can be used for primarily and quickly removing an oxide layer on the surface of a cathode roller, but the roughness of the roller surface of electrolytic copper foil separated out on the ground cathode roller is higher; on the contrary, when the number of the types of the grinding wheels is larger, the larger the number represents that the grain size of the grinding particles is smaller, the electrolytic copper foil is suitable for fine polishing, and the roll surface of the electrolytic copper foil precipitated on the cathode roll after the fine polishing has higher brightness and lower roughness. Preferably, the brightness of the roller surface of the electrolytic copper foil is between 35 and 65.

The electrolytic copper foil according to the present invention has 34 kilograms per square millimeter (kgf/mm) at a drawing speed of 50 millimeters per minute (mm/min)²) The above tensile strength. When the electrolytic copper foil is applied to a lithium ion secondary battery, an active material is coated on the surface of the electrolytic copper foil, and then processes such as rolling and slitting are performed. Preferably, the electrolytic copper foil has a tensile strength of 34.1kgf/mm²To 34.8kgf/mm²。

The surface roughness of the electrolytic copper foil according to the present invention is expressed as 10-point average roughness (Rz) specified in JIS B0601-. When the surface of the electrolytic copper foil is smoother (namely, Rz is smaller), the finer the crystallization on the surface of the electrolytic copper foil is, the surface area of the electrolytic copper foil can be increased, and the current can be increased; however, if the surface of the electrolytic copper foil is too smooth, the adhesion of the active material to the electrolytic copper foil may be reduced, which may cause delamination and affect the performance of the battery. The surface roughness may be greater than or equal to 1.0 micrometers (μm) and less than or equal to 2.5 μm, preferably greater than or equal to 1.2 μm and less than or equal to 2.0 μm, for the roll surface; the surface roughness of the deposition surface may be 1.0 μm or more and 3.0 μm or less, and preferably 1.4 μm or more and 2.0 μm or less.

The nano-indentation hardness of the deposition surface of the electrolytic copper foil according to the invention can be between 1.5GPa and 2.0 GPa.

The thickness of the electrolytic copper foil according to the present invention is not particularly limited, and preferably, the thickness is from 3 μm to 105 μm; more preferably, the thickness is between 5 μm and 30 μm.

In order to achieve the purpose of improving functions such as rust prevention, common surface treatment can be carried out on the electrolytic copper foil according to requirements; for example, the surface of the electrolytic copper foil may be subjected to one or more surface treatments such as an anti-rust treatment and a silane coupling treatment, but is not limited thereto. Accordingly, at least one of the roll surface or the deposition surface of the electrolytic copper foil may further include a rust preventive layer or a silane coupling agent layer.

As the rust-preventive treatment, there can be mentioned an organic rust-preventive treatment using azole compounds (azole) or the like or an inorganic rust-preventive treatment using chromate or the like, and at least one of the roll surface or the deposition surface of the electrolytic copper foil may further include an organic rust-preventive layer or an inorganic rust-preventive layer; the rust preventive element can be attached to the surface of the electrolytic copper foil by dip coating, spray coating, plating, or the like. Examples of the azole compound include triazole compounds such as triazole, benzotriazole, tolyltriazole, carboxybenzotriazole, chlorine-substituted benzotriazole, 3-amino-1, 2, 4-triazole, 4-amino-1, 2, 4-triazole, and derivatives thereof; thiazole compounds such as thiazole, isothiazole, 2-amino-4-methylthiazole, and derivatives thereof; imidazole compounds such as imidazole, 1-methyl-2-mercaptoimidazole, 1- (. beta. -hydroxyethyl) -2-methylimidazole, 1- (. beta. -chloroethyl) -2-methylimidazole, 2-aminobenzimidazole, or derivatives thereof; the organic rust-preventive treatment can be carried out using one or more of the above-mentioned azole compounds.

The silane coupling treatment is to carry out surface treatment on the surface of the electrolytic copper foil by using a silane coupling agentThe silane coupling agent may include, but is not limited to, the group represented by the following chemical formula: y- (R')_n-Si(OR)₃Wherein Y is selected from the group consisting of glycidyl (epoxy), amino, epoxycyclohexyl, ureido, carbamate, malonate, carboxyl, mercapto, cyano, acetoxy, acryloxy, methacryloxy, chloromethylphenyl, pyridyl, vinyl, dialkylamino, phenylalkylamino, and imidazolyl; n is an integer of 0 or 1; r' is an ethylene, propylene, or ethylene or propylene substituted phenylene group wherein the benzene ring in the phenylene group is attached to Y; and R is methyl, ethyl, or C3-6 linear or branched alkyl; specifically, the silane coupling agent may be an epoxy silane, an amino silane, a methacryloxy silane, a vinyl silane, or a mercapto silane; the silane coupling treatment may also be performed using more than one silane coupling agent.

In addition, the invention also provides an electrode for a lithium ion battery, which comprises the electrolytic copper foil. Preferably, the electrode is a negative electrode.

Specifically, the electrode further comprises at least one adhesive and at least one active material. For example, the adhesive may include polyvinylidene fluoride (PVDF), polyacrylic acid (poly (acrylic acid)), carboxymethyl cellulose (CMC), Styrene Butadiene Rubber (SBR), Polyimide (PI), polyvinyl alcohol (polyvinyl alcohol), or a combination thereof, but is not limited thereto.

The electrolytic copper foil is particularly suitable for use as a negative electrode current collector which is suitable for use in a lithium ion secondary battery; generally, the electrolytic copper foil is coated with a negative active material (or simply "active material") on one side or both sides. The active material may form one or more layers on or around the anode current collector, and generally comprises a carbon material.

The active material can provide the electrode with good cycle characteristics. For example, the active material may be a carbon material, a silicon material, a metal oxide, a metal alloy, or a polymer, with a carbon material or a silicon material being preferred. Specifically, the carbon material may be non-graphitic carbon (non-graphite carbon), coke (coke), graphite (graphite), glassy carbon (glass carbon), carbon fiber (carbon fiber), activated carbon (activated carbon), carbon black (carbon black), or a high polymer calcined material, but is not limited thereto; wherein the coke comprises pitch coke, needle coke or petroleum coke; the high polymer calcined material is a material obtained by firing a high polymer material such as phenol-formaldehyde resin (phenol-formaldehyde resin) or furan resin (furan resin) at an appropriate temperature so as to be carbonated. The silicon material can be used as a negative electrode active material having an excellent ability to form an alloy together with lithium ions and an excellent ability to extract lithium ions from the alloy lithium, and when the silicon material is used to form a lithium ion secondary battery, a secondary battery having a large energy density can be realized; the silicon material may be used In combination with cobalt (Co), iron (Fe), tin (Sn), nickel (Ni), copper (Cu), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), chromium (Cr), ruthenium (Ru), molybdenum (Mo), or combinations thereof to form an alloy material. The elements of the metal or metal alloy may be selected from the group consisting of: cobalt (Co), iron (Fe), tin (Sn), nickel (Ni), copper (Cu), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb), chromium (Cr), ruthenium (Ru), and molybdenum (Mo), but are not limited thereto. Examples of the metal oxide are, but not limited to, iron sesquioxide, iron tetraoxide, ruthenium dioxide, molybdenum dioxide, and molybdenum trioxide. Examples of such polymers are polyacetylene (polyacetylene) and polypyrrole (polypyrrole), but are not limited thereto.

In addition, other auxiliary additives, such as lithium hydroxide (LiOH), oxalic acid (H), etc., may also be added to the electrode according to different usage requirements without affecting the effect of the electrode for lithium ion batteries of the present invention₂C₂O₄) And the like, but not limited thereto.

In addition, the present invention also provides a lithium ion battery comprising: the electrode, the positive electrode and the electrolyte for the lithium ion battery are provided. In some embodiments, the lithium ion battery is separated between the positive electrode and the negative electrode by a separator.

Specifically, the electrolyte may include a solvent and an electrolyte dissolved in the solvent, and may further include additives, if necessary. The solvent includes non-aqueous solvents such as: cyclic carbonates such as Ethylene Carbonate (EC) and Propylene Carbonate (PC); chain carbonates such as dimethyl Carbonate (DMC), diethyl Carbonate (DEC) and Ethyl Methyl Carbonate (EMC); or sultone, but is not limited thereto; the solvents may be used alone, or two or more solvents may be used in combination; for example, when a solvent having a high dielectric constant (e.g., ethylene carbonate or propylene carbonate) and a solvent having a low viscosity (e.g., dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate) are used in combination, a high dissolving power for an electrolyte and a high ion conductivity can be achieved.

The electrolyte may be used as it is or in a form of mixing the electrolyte with a polymer material to make a gel electrolyte. The separator may be impregnated in the electrolyte, or the electrolyte may be provided in the separator and a layer between the negative electrode and the positive electrode. Preferred polymeric materials are, for example, vinylidene fluoride-containing polymers, because of their high redox stability; in some embodiments, the polymeric material may also be formed from a monofunctional acrylate, such as an acrylate; monofunctional methacrylates, such as methacrylate; multifunctional acrylates, such as diacrylates and triacrylates; multifunctional methacrylates such as dimethacrylate and trimethacrylate; acrylonitrile; and a monomer of a polymer such as methacrylonitrile; preferably, the polymer material is polymerized from a polymer monomer having an acrylate group or a methacrylate group, which is easily polymerized and has high polymerization reactivity.

There is no particular limitation regarding the structure or type of the lithium ion battery, and the lithium ion battery may be a stack type including a negative electrode and a positive electrode stacked by a separator or a spiral wound type including a continuous electrode and a separator spirally wound together. The form of the lithium ion battery is not particularly limited, and the lithium ion battery may be a cylindrical secondary battery widely used for a notebook Personal Computer (PC) or the like, a rectangular parallelepiped secondary battery used for a mobile phone, a button secondary battery, or a coin secondary battery. As the sealing material used in the secondary battery, a typical aluminum can, stainless steel can, double layer film, or the like may be used, but is not limited thereto.

Drawings

FIG. 1 is a schematic view of a process for electrolytic copper foil.

Detailed Description

Hereinafter, those skilled in the art can easily understand the advantages and effects of the present invention from the following examples. Therefore, it is to be understood that the description set forth herein is intended merely to illustrate preferred embodiments and not to limit the scope of the invention, which can be modified and varied to practice or apply the teachings of the present invention without departing from the spirit and scope thereof.

The following examples used instrument models:

1. nano-indentation system: MTS Nano introducer XPW SYSTEM XPW 291;

2. a light splitting type color difference meter: CM-2500c manufactured by Konica Minolta;

3. type α surface roughness meter: SE 1700 manufactured by Kosaka Laboratory;

4. a tensile testing machine: AG-I manufactured by SHIMADZU Corporation;

5. a rolling machine: BCR-250 manufactured by Shyh horning Machinery industry;

6. the battery charge and discharge test host: series 4000 by Maccor.

The following examples used the starting materials:

1. low molecular weight bone glue DV: available from Nippi inc;

2. sodium 3-mercapto-1-propanesulfonate: purchased from Hopax Chemicals Manufacturing Company Ltd;

3. hydrochloric acid: purchased from RCI Labscan ltd.;

4. thiourea: purchased from Panreac quiimica SAU;

5. carbon black: super

Purchased from UBIQ technology.

Preparation of electrolytic copper foil

Preparing a copper sulfate electrolyte of the electrolytic bath:

dissolving copper wire in 50 wt% sulfuric acid water solution to obtain copper sulfate (CuSO)₄·5H₂O) a base solution having a concentration of 320 grams per liter (g/L) and a sulfuric acid concentration of 100 g/L. Then, in the basic solution, 5.5 milligrams (mg) of low-molecular-weight bone glue DV, 3mg of 3-mercapto-1-propane sodium sulfonate (MPS), 0.01mg of thiourea and 25mg of hydrochloric acid are added per liter of the basic solution to prepare a copper sulfate electrolyte.

Electrolytic copper foil of example 1

Referring to fig. 1, before cathode drum 10 is immersed in copper sulfate electrolyte 30 of the electrolytic bath, a spraying device 40 having an elevation angle of 45 degrees and a distance of about 5 cm from cathode drum 10 is used to spray a pre-bath spraying liquid 401 having a temperature of 55 ℃ onto the surface of cathode drum 10 not immersed in the electrolytic bath in a parabolic spraying manner with a spraying flow rate of 5 liters/minute (L/min), wherein the composition and concentration of copper sulfate electrolyte 30 in the pre-bath spraying liquid 401 and the electrolytic bath are the same. Meanwhile, a polishing Wheel 50 (a Kure Grinding Wheel company, model 2000) is rotated in a single direction at a rotation speed of 300rpm and a linear velocity of 1 meter/minute (m/min) of the cathode roll 10, and the cathode roll 10 is mechanically polished by the polishing Wheel 50 to remove impurities on the cathode roll 10; the pressure applied to the cathode roll 10 by the polishing wheel 50 was controlled by a load current of a polishing rotary driving motor (not shown), and the current was set to 1.2 amperes (a). And a current density of 50 amperes per square decimeter (A/dm) in an electrolytic bath at 50 DEG C²) Flows between the cathode roll 10 and the anode plate 20 disposed along the shape of the cathode roll 10 so that copper ions in the copper sulfate electrolyte 30 are precipitated on the surface of the cathode roll 10 to form an electrolytic copper foil 70, and then, the cathode roll 10 is rotated to form a cathode rollThe electrolytic copper foil 70 was peeled off from the cathode roll 10 by a series of guide rolls 60 and wound up to obtain an electrolytic copper foil 70 having a thickness of 8 μm. The electrodeposited copper foil 70 has opposing roll 701 and deposition 702 surfaces. In some cases, subsequent processing treatments may also be performed, such as surface roughening, rust prevention, metal or metal alloy plating, and the like. The rust-preventive treatment can be carried out by using a chromic acid solution having a chromic acid concentration of 1.5g/L at 31.5 ℃ and a current density of 0.5A/dm²Forms an inorganic rust preventive layer including chromate on the roll surface 701 and the deposition surface 702.

Electrolytic copper foil of example 2

The method used for preparing example 2 was similar to the method used for preparing the electrolytic copper foil of example 1, with the difference that: the model 2000 polishing wheel used in example 1 was changed to the model 1500 polishing wheel, and the temperature of the liquid sprayed before the bath in example 1 was changed from 55 ℃ to 45 ℃.

Electrolytic copper foil of example 3

The method used for preparing example 3 was similar to the method used for preparing the electrolytic copper foil of example 1, with the difference that: the spray flow rate used in example 1 was changed from 5L/min to 10L/min.

Electrolytic copper foil of example 4

The method used for preparing example 4 was similar to the method used for preparing the electrolytic copper foil of example 2, with the difference that: the spray flow rate used in example 2 was changed from 5L/min to 10L/min.

Electrolytic copper foil of example 5

The method used for preparing example 5 was similar to the method used for preparing the electrolytic copper foil of example 4, with the difference that: the spray flow rate used in example 4 was changed from 10L/min to 20L/min and the temperature of the pre-bath spray of example 4 was changed from 45 ℃ to 55 ℃.

Electrolytic copper foil of example 6

The method used for preparing example 6 was similar to the method used for preparing the electrolytic copper foil of example 1, with the difference that: the spray flow rate used in example 1 was changed from 5L/min to 20L/min, and the temperature of the spray solution before the tank of example 1 was changed from 55 ℃ to 45 ℃.

Electrolytic copper foil of comparative example 1

The preparation method used was the same as that of example 2 for polishing the cathode roll and electrodepositing the electrolytic copper foil, but the cathode roll was not sprayed with the pre-bath spray. The method mainly comprises the following steps: before the cathode drum was immersed in the copper sulfate electrolyte of the electrolytic bath, a buffing Wheel (Kure Grinding Wheel company, model 1500) was rotated in a single direction at a rotational speed of 300rpm and a linear speed of 1m/min of the cathode drum, and the cathode drum was mechanically buffed by the buffing Wheel; the pressure applied to the cathode drum by the polishing wheel was controlled by the load current of the polishing rotary drive motor, which was set to 1.2A. And, in an electrolytic bath at 50 ℃, at a current density of 50A/dm²The current of (2) was flowed between a cathode roll and an anode plate disposed along the shape of the cathode roll, so that copper ions in a copper sulfate electrolyte were precipitated on the surface of the cathode roll to form an electrolytic copper foil, and then, the electrolytic copper foil was peeled off from the cathode roll by a series of guide rolls and rolled up to obtain an electrolytic copper foil having a thickness of 8 μm.

Electrolytic copper foil of comparative example 2

The method used to prepare comparative example 2 was similar to the method used to prepare the electrolytic copper foil of example 3, with the difference that: the temperature of the spray solution before the tank of example 3 was changed from 55 ℃ to 70 ℃.

Electrolytic copper foil of comparative example 3

The method used to prepare comparative example 3 was similar to the method used to prepare the electrolytic copper foil of example 4, with the difference that: the temperature of the spray solution before the tank of example 4 was changed from 45 ℃ to 30 ℃.

Electrolytic copper foil of comparative example 4

The method used to prepare comparative example 4 was similar to the method used to prepare the electrolytic copper foil of example 3, with the difference that: the spray flow rate used in example 3 was changed from 10L/min to 1L/min.

Electrolytic copper foil of comparative example 5

The method used to prepare comparative example 5 was similar to the method used to prepare the electrolytic copper foil of example 5, with the difference that: the spray flow rate used in example 5 was changed from 20L/min to 50L/min.

Electrolytic copper foil of comparative example 6

The method used to prepare comparative example 6 was similar to the method used to prepare the electrolytic copper foil of example 6, with the difference that: the spray flow rate used in example 6 was changed from 20L/min to 65L/min.

Electrolytic copper foil of comparative example 7

The method used to prepare comparative example 7 was similar to the method used to prepare the electrolytic copper foil of example 6, with the difference that: the model 2000 polishing wheel used in example 6 was changed to a model 1000 polishing wheel.

Electrolytic copper foil of comparative example 8

The method used to prepare comparative example 8 was similar to the method used to prepare the electrolytic copper foil of example 6, with the difference that: the model 2000 polishing wheel used in example 6 was changed to a model 2500 polishing wheel.

Analysis 1: nanoindentation surface hardness analysis

The electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 were analyzed for surface hardness using a nanoindentation system. The nanoindentation system is matched with a Berkovich pressure head with the curvature radius less than or equal to 50 nanometers (nm), and is pressed down at the speed of 0.04 millimeter/second; because the hardness value measured by initial pressing is higher due to the interference of uneven surface flatness, and the hardness value gradually becomes stable as the indentation depth gets deeper and deeper, the hardness value is regarded as the real sample hardness value, so the invention analyzes the surface hardness of the roller surface and the deposition surface of the electrolytic copper foil when the indentation depth is 300nm, and arranges the experimental result in the following table 1.

Analysis 2: surface brightness analysis

The electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 were analyzed for roll-to-roll brightness based on JIS Z8722 (2000) method using a spectroscopic colorimeter (Konica Minolta; CM2500c) in a "measurement method of color-reflection and transmission object color" mode, and the experimental results are collated in the following table 1.

Analysis 3: surface roughness analysis

The electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 were analyzed for surface roughness on an alpha-type surface roughness meter. Rz of the roll surface and the deposition surface of these electrolytic copper foils were measured respectively in accordance with the method prescribed in JIS B0601-1994, and the experimental results are collated in the following table 1.

Analysis 4: tensile Strength analysis

The electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 were each cut into test samples having a size of 100 mm × 12.7 mm, and the test samples representing the electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8, respectively, were measured with a tensile tester at about 25 ℃ under the conditions of a chuck distance of 50mm (mm) and a crosshead speed (crosscut speed) of 50mm/min according to the method specified in IPC-TM-6502.4.18, and the experimental results are collated in table 1 below.

Table 1: results of analyzing characteristics of the electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8

As shown in the above table 1, it can be seen from the results of examples 1 to 6 compared to comparative example 1 that, before the cathode roller is immersed in the copper sulfate electrolyte of the electrolytic bath, the pre-bath spray liquid is sprayed onto the cathode roller in advance, and then immersed in the electrolytic bath, so that a thin electrolyte layer can be formed on the cathode roller in advance, which contributes to increasing the surface coverage of nucleation points during electrolysis, so that each point on the surface of the cathode roller can have a relatively uniform energizing effect, and the growth rate of copper crystal lattices at different positions can be relatively uniform, thereby increasing the surface hardness of the roller surface of the electrolytic copper foil.

In addition, as can be seen from the results of examples 1 to 6 compared to comparative examples 2 to 8, the spraying flow rate, the temperature of the spraying liquid before the bath and the type of the polishing wheel set by the process also affect the characteristics of the electrolytic copper foil. When the spraying flow is too low, the effect of improving the hardness of the roller surface of the electrolytic copper foil is not obvious due to insufficient thickness or too small area of the spraying liquid before being sprayed to the groove on the surface of the cathode roller; on the other hand, when the spraying flow rate is too high, the effect of increasing the hardness of the roll surface of the electrolytic copper foil is also poor because many bubbles adhere to the sprayed liquid before being sprayed to the grooves of the cathode roll surface. Preferably, the spraying device sprays the liquid before the groove onto the surface of the cathode roller at a spraying flow rate of 1L/min to 65L/min, and more preferably, the spraying flow rate is 5L/min to 20L/min. When the temperature of the spraying liquid before the tank is too low, nucleation points are not formed, so that the hardness of the roller surface of the electrolytic copper foil is improved to be insufficient; on the other hand, when the temperature of the liquid sprayed before the bath is too high, the surface of the cathode roll is easily oxidized, resulting in a decrease in the brightness of the roll surface of the electrolytic copper foil. Preferably, the temperature of the spraying liquid before the tank is between 30 ℃ and 70 ℃, and more preferably, the temperature of the spraying liquid before the tank is between 45 ℃ and 55 ℃. When the model of the polishing wheel is too low, the brightness of the roll surface of the prepared electrolytic copper foil is too low; on the other hand, when the size of the polishing wheel is too large, the brightness of the roll surface of the obtained electrolytic copper foil is too high. Preferably, the polishing wheels are 1500 and 2000.

Negative electrodes of examples 7 to 12 and comparative examples 9 to 16, and lithium ion batteries including the same

Negative electrodes of examples 7 to 12 and comparative examples 9 to 16 were prepared under the same conditions as below, using the electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 in this order.

Forming a negative electrode slurry by 100 parts by weight of a negative electrode solid material and 60 parts by weight of N-methylpyrrolidone (NMP); wherein, based on the total weight of the cathode solid material, the content of mesocarbon Graphite Microspheres (MGP) as the cathode active material is 93.9 wt%, the content of carbon black is 1 wt%, the content of polyvinylidene fluoride (PVDF 6020) is 5 wt%, and the content of oxalic acid is 0.1 wt%.

Then, the above-mentioned negative electrode slurry was coated on the electrolytic copper foils of examples 1 to 6 and comparative examples 1 to 8 at a speed of 5m/min, respectively, to a thickness of 200 μm, and then dried at a temperature of 160 ℃, thereby forming negative electrodes of examples 7 to 12 and comparative examples 9 to 16, respectively.

Analysis 5: roll compaction test

The negative electrodes of examples 7 to 12 and comparative examples 9 to 16 were subjected to a rolling test using a roller of 250mm diameter, rockwell Hardness (HRC) of 62 to 65 degrees, and high carbon chromium bearing steel (SUJ2) as a material, at a rolling speed of 1m/min and a pressure of 3000 pounds force per square inch (psi), and whether or not the interface between the electrolytic copper foil and the negative electrode slurry was broken in the negative electrodes of examples 7 to 12 and comparative examples 9 to 16 was observed, and the experimental results are collated in table 2 below.

Lithium ion batteries including the negative electrodes of examples 7 to 12 and comparative examples 9 to 16 were prepared under the same conditions as follows, using the negative electrodes of examples 7 to 12 and comparative examples 9 to 16 in this order.

Taking the preparation of a lithium ion battery comprising the negative electrode of example 7 as an example: forming positive electrode slurry by 100 parts by weight of a positive electrode solid material and 195 parts by weight of NMP; wherein, based on the total weight of the anode solid material, the anode active material (LiCoO)₂) In an amount of 89 wt%, Flaked graphite (KS 6) in an amount of 5 wt%, and conductive carbon black powder (Super)

) Is used in an amount of 1 wt%, and polyvinylidene fluoride (PVDF 1300) is used in an amount of 5 wt%.

And then, coating the positive electrode slurry on an aluminum foil until the thickness is 250 mu m, and drying at 160 ℃ to form a positive electrode.

The positive electrode and the negative electrode of example 7 were alternately stacked with a microporous separator (manufactured by Celgard corporation) interposed therebetween, and then placed in a press-fit mold filled with an electrolyte (a volume ratio of ethylene carbonate to dimethyl carbonate is 1:1) to seal and form a laminated lithium ion battery having dimensions of 41mm × 34mm × 53 mm.

Analysis 6: battery cycle life analysis

Charge and discharge cycle tests were performed at 55 ℃ using these lithium ion batteries comprising the negative electrodes of examples 7 to 12 and comparative examples 9 to 16: the measurement was performed in a constant current-constant voltage (CCCV) charging mode and a Constant Current (CC) discharging mode, wherein the charging voltage was 4.2 volts (V) and the charging current was 5C; the discharge voltage was 2.8V and the discharge current was 5C. The cycle life is defined as the number of charge and discharge cycles performed by the tested lithium ion battery when its capacity drops to 80% of the initial capacity. For example, the lithium ion battery including the negative electrode of example 7 had a rated capacity of 80% of the initial capacity after the sub-charge-discharge cycle was performed.

Table 2: crush test of negative electrodes of examples 7 to 12 and comparative examples 9 to 16 and test result of cycle life of lithium ion batteries including negative electrodes of examples 7 to 12 and comparative examples 9 to 16

The above analysis results show that the roll surfaces of the electrodeposited copper foils of examples 1 to 6 have both an appropriate surface hardness range and an appropriate brightness range, and therefore, the negative electrodes of examples 7 to 12 fabricated using the electrodeposited copper foils of examples 1 to 6 do not break during the roll test, showing that the negative electrodes have good mechanical properties. Moreover, the lithium ion batteries including the negative electrodes of examples 7 to 12 indeed had good cycle characteristics as confirmed by the charge and discharge tests of the lithium ion batteries, and the lithium ion batteries could have a long battery life.

In contrast to the negative electrodes of comparative examples 9 to 16 produced from the electrolytic copper foils of comparative examples 1 to 8, the electrolytic copper foils of comparative examples 1, 3 to 5 still had the problem of breakage after rolling, but the electrolytic copper foils of comparative examples 2, 6 to 8 passed the rolling test, but still had the problem of poor cycle life, because the surface hardness and brightness of the roll surface of the electrolytic copper foils of these comparative examples were not controlled within the appropriate ranges at the same time.

Moreover, when the electrolytic copper foils of embodiments 1 to 6 are manufactured, the roll surfaces of the electrolytic copper foils of embodiments 1 to 6 can have both an appropriate surface hardness range and an appropriate brightness range without repeating a plurality of foil manufacturing processes, and the requirements for the lithium ion battery can be met, so that the electrolytic copper foils have the advantages of simple process and higher development potential.

The above embodiments are merely exemplary for convenience of description, and the embodiments are not intended to limit the scope of the invention; it is intended that all such alterations, modifications, and other changes which come within the spirit of the disclosure be embraced therein without departing from the scope of the disclosure.

Claims

1. An electrolytic copper foil having a roll surface and a deposition surface opposed to each other; wherein the nanoindentation surface hardness of the roll face is equal to or greater than 0.5 gigapascals and equal to or less than 3.5 gigapascals; and the lightness of the roll surface is equal to or greater than 25 and equal to or less than 75.

2. The electrolytic copper foil according to claim 1, wherein the nanoindentation surface hardness of the roll surface is equal to or greater than 1.0 gigapascal and equal to or less than 3.0 gigapascal.

3. The electrolytic copper foil according to claim 1, wherein the tensile strength of the electrolytic copper foil is 34 kg/mm or more.

4. The electrolytic copper foil according to claim 1, wherein at least one of the roll surface or the deposition surface further comprises an inorganic rust preventive layer.

5. The electrolytic copper foil according to claim 4, wherein the inorganic rust preventive layer comprises a chromate.

6. The electrolytic copper foil according to claim 1, wherein at least one of the roll surface or the deposition surface further comprises an organic rust preventive layer.

7. The electrolytic copper foil according to claim 6, wherein the organic rust preventive layer comprises an azole-based compound.

8. An electrode for a lithium ion battery comprising the electrodeposited copper foil as set forth in any one of claims 1 to 7, at least one adhesive and at least one active material.

9. The electrode of claim 8, wherein the active material comprises a carbon material, a silicon material, a metal oxide, a metal alloy, a polymer, or combinations thereof.

10. A lithium ion battery comprising the electrode for a lithium ion battery according to claim 8 or 9, a positive electrode and an electrolyte, the electrode being a negative electrode.